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Laboratory of Neuromodulation and Behavior

Meeting Abstracts


Title:Modafinil blocks morphine-primed reinstatement of conditioned place preference
Location:Hall A-C
Presentation Time:Saturday, Nov 15, 2008, 2:00 PM - 3:00 PM
Authors:*P. TAHSILI-FAHADAN1, G. V. CARR2, G. C. HARRIS2, G. ASTON-JONES1;
1Dept. of Neurosci., MUSC, Charleston, SC; 2Dept. of Psychiatry, Univ. of Pennsylvania, Philadelphia, PA
Abstract:

Opiate addiction is a chronic disorder characterized by high rates of relapse following long periods of abstinence. This problem requires new relapse-prevention treatments that do not have abuse potential. Recently, it has been shown that the wake-promoting drug modafinil may be an effective treatment for cocaine addiction. In this study, we investigated the effects of modafinil pretreatment on reinstatement of extinguished morphine conditioned place preference (CPP) as an animal model of relapse. Sprague-Dawley rats were trained to acquire CPP for morphine (8 mg/kg, ip), and after extinction of the CPP, the expression of place preference was reinstated by a morphine priming injection (8 or 16 mg/kg, ip). Pretreatment with modafinil (300 mg/kg, ip) 30 min prior to the morphine priming injection blocked reinstatement of CPP. However, pretreatment with a lower dose of modafinil (100 mg/kg) did not alter morphine-primed reinstatement of CPP. Additional experiments showed that modafinil (300 mg/kg) did not produce CPP by itself and did not alter the expression of morphine CPP in the presence or absence of morphine (8 mg/kg). In conclusion, our results indicate that modafinil may be an effective agent in the treatment of relapse to opiate abuse.

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Title:Influence of the orexin / hypocretin system on alcohol preference in Sprague Dawley rats
Location:Hall A-C
Presentation Time:Saturday, Nov 15, 2008, 4:00 PM - 5:00 PM
Authors:*D. E. MOORMAN, P. T. KNACKSTEDT, G. ASTON-JONES;
Neurosciences, Med. Univ. South Carolina, Charleston, SC
Abstract:

Our lab has shown that orexin (ORX, or hypocretin) neurons in lateral hypothalamus (LH) are involved in morphine, cocaine, and food preference (Harris et al, 2005). Other groups have demonstrated a connection between the ORX system and ethanol (EtOH)-related behaviors (Lawrence et al. 2006, Dayas et al. 2007). Here we extend those results to investigate, in Sprague Dawley rats, the relationship between EtOH preference and the ORX system using three different techniques. In each series of studies, rats were trained to drink 10% EtOH using either sucrose fade or intermittent exposure. Both methods produced significant EtOH consumption (> 2 g/kg/2 hrs). Preference varied across but was stable within individuals.
Expt. (1) After sucrose fade and EtOH consumption (2 hrs/day, 2 weeks), 16 rats were tested for EtOH vs. water preference using a conditioned place preference (CPP) paradigm. Following CPP testing, LH sections were stained for ORX and Fos. Across a majority of rats, we found a correlation between Fos-labeled ORX neurons and EtOH CPP scores (r = 0.62, p<0.05). We also found a relationship between the number of immunoreactive ORX neurons present in each rat and the average daily EtOH that the rat consumed pre-conditioning (r = 0.55, p<0.05).
Expt. (2) After intermittent exposure, 8 rats were tested for EtOH preference characterized by EtOH:water consumption ratios in a 2-bottle choice test (2 hrs/day). During testing, rats were treated with the Ox1 receptor antagonist SB-334867 (SB; 30 mg/kg, ip). SB blocked EtOH (but not water) preference in EtOH preferrers, but not in non-preferrers.
Expt. (3) After sucrose fade, 8 rats were tested for EtOH preference using a 2-bottle choice test. Following 2-bottle testing, rats were anesthetized, and LH neurons were juxtacellularly recorded and labeled with the goal of characterizing the responses of LH ORX and non-ORX neurons to EtOH or EtOH-associated cues. Preliminary results from naïve animals indicate that putative ORX neurons in LH are robustly modulated (both activated and inhibited) by directly applied EtOH and are weakly and transiently activated by EtOH-associated cues.
These results extend previous findings to demonstrate a relationship between the ORX system and EtOH preference in individual Sprague Dawley rats. Based on our preliminary data, we hypothesize a relationship between EtOH preference and ORX expression and neuronal activation, consistent with other evidence for a role of LH ORX neurons in drug-seeking and addiction. These findings highlight the ORX system as a potential target for treatment for multiple drugs of abuse.

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Title:Afferents that regulate lateral hypothalamic orexin / hypocretin neurons during drug seeking behaviors
Location:Hall A-C
Presentation Time:Saturday, Nov 15, 2008, 1:00 PM - 2:00 PM
Authors:*G. C. SARTOR, G. ASTON-JONES;
Dept. of Neurosciences, MUSC, Charleston, SC
Abstract:

Recent results in our lab revealed that lateral hypothalamic (LH) orexin (hypocretin) afferents to the ventral tegmental area are importantly involved in reward processing. In particular, Harris et al. (2005) found that LH orexin neurons are Fos-activated by conditioned stimuli associated with drugs or food, and that activation of these neurons reinstates extinguished morphine-seeking, measured in a preference test. However, the circuitry that gates the activation of LH orexin neurons during drug-seeking behaviors has yet to be elucidated. In the current project, we combined tract tracing techniques with cocaine-conditioned place preference (CPP), and staining for the immediate early gene product Fos, to identify LH orexin inputs that are activated during cocaine preference. The retrograde tracer cholera toxin b (CTb) was injected (30 nl) into the LH orexin field, and rats were then conditioned for cocaine CPP (10 mg/kg). Two hours after the CPP test session (drug-free), rats were perfused with 4% paraformaldehyde, and their brains were sectioned and immunohistochemically stained for Fos and CTb. Preliminary results revealed several brain areas that have strong inputs to the LH orexin field (prelimbic cortex, infralimbic cortex, lateral septum, nucleus accumbens shell, bed nucleus of stria terminalis, and lateral preoptic area), consistent with previous findings. However, only the lateral septum and ventral bed nucleus of stria terminalis showed a significant increase in Fos+ retrogradely labeled neurons during cocaine preference. Future studies will determine which LH orexin afferents are critical for Fos induction in orexin neurons during drug preference, and for the acquisition and/or expression of CPP for cocaine.

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Title:The orexin / hypocretin 1 receptor antagonist SB-334867 reduces cocaine-seeking in rats after 1 or 14 days of abstinence
Location:Hall A-C
Presentation Time:Saturday, Nov 15, 2008, 2:00 PM - 3:00 PM
Authors:*R. J. SMITH1,2, G. ASTON-JONES1;
1Neurosciences, Med. Univ. South Carolina, Charleston, SC; 2Neurosci. Grad. Group, Univ. Pennsylvania, Philadelphia, PA
Abstract:

We previously showed that signaling at the orexin (hypocretin) 1 receptor is critical for cue-induced reinstatement of extinguished cocaine-seeking in a self-administration paradigm (SFN 2007). Here, we tested whether the orexin system is involved in drug-seeking behavior during initial extinction responding. Male Sprague-Dawley rats self-administered intravenous cocaine paired with discrete tone and light cues for 10 days (0.2 mg/infusion, FR1 schedule, 2 hours/day). Animals were then given an extinction trial (no cocaine, no cues) on the subsequent day or following 14 days of forced abstinence in the home cage. Lever-pressing following abstinence for 1 or 14 days is typically elevated and reflects drug-seeking driven by the drug-associated context. Pretreatment with 30 mg/kg (ip) of the orexin 1 receptor antagonist SB-334867 (SB) significantly reduced lever-pressing after 1 or 14 days of abstinence as compared to vehicle pretreatment. Animals tested after 1 day of abstinence were given a total of 7 extinction sessions, in which only the first day included SB or vehicle pretreatment. Across the 6 untreated extinction sessions, the post-SB group showed a rebound of responding and then a gradual tapering that paralleled the vehicle group. On the seventh day, the two groups showed a similar low level of responding. When the first and seventh days were compared, the vehicle group showed significant extinction but the SB group showed no difference in responding. This indicates that SB blocked the elevated responding observed during initial extinction. Taken together with prior results, these data indicate that orexin signaling is necessary for cocaine-seeking elicited by discrete cues or by contexts previously associated with the drug.

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Title:Lateral versus medial hypothalamic orexin / hypocretin neurons: Bi-directional influence on ventral tegmental area neurons in vivo
Location:Hall A-C
Presentation Time:Saturday, Nov 15, 2008, 3:00 PM - 4:00 PM
Authors:*L. MASSI, D. E. MOORMAN, G. ASTON-JONES;
Neurosciences, Med. Univ. of South Carolina, Charleston, SC
Abstract:Recent work has shown that orexin (hypocretin) in the ventral tegmental area (VTA) is critical for the induction of synaptic plasticity and the control of reward-driven behavior, including behaviors related to drugs of abuse. Our lab reported evidence that orexin neurons in the lateral hypothalamus (LH) regulate reward processing for food and drugs of abuse whereas those located in the medial hypothalamus (MH) are involved in arousal and response to stress (Harris et al, Nature 2005). However, the influence of orexin neurons in the LH and MH on impulse activity of neurons in VTA is poorly understood. In this study we recorded from single VTA neurons in anesthetized rats during stimulation of orexin neurons by local microinjection of rat pancreatic polypeptide (rPP) into LH or MH. Stimulation of orexin cell fields in LH and MH produced different responses on VTA neuronal actvity: Stimulation of LH with rPP inhibited (39/108) or activated (3/108) putative DA neurons, and activated (9/42) or inhibited (3/42) putative GABA neurons. In contrast, rPP microinjection in MH activated (16/108) or inhibited (4/108) DA neurons, and inhibited (13/42) or activated (2/42) GABA cells. Typically, neurons that were responsive to LH were not responsive to MH stimulation, and vice versa. These responses were blocked by local application of the Ox1 receptor antagonist SB334867 (SB; 10 μM, 60 nl) in VTA from a pipette barrel adjacent to the recording pipette, supporting the involvement of the orexin system. To test whether LH stimulation may indirectly inhibit DA neurons via local GABA interneurons, we applied picrotoxin (PTX; 1 mM, 60 nl) onto VTA DA neurons using a double barrel micropipette and monitored their responses to LH rPP. We found that intra-VTA PTX activated VTA DA neurons and blocked inhibition of these neurons induced by rPP in LH (n=11 neurons). The PTX-induced increase in VTA DA firing rate was higher when PTX was accompanied by rPP intra-LH, possibly due to the effect of orexin release onto DA neurons. Our results indicate that orexin neurons in LH and MH may regulate the activity of different populations of VTA neurons in opposite ways. Taken as a whole, this study supports a dichotomy in orexin function with MH and LH orexin neurons differently regulating VTA DA neurons and behavioral functions.
Title:Activation of VTA-projecting orexin / hypocretin neurons in the lateral, but not the dorsomedial and perifornical hypothalamus, correlates with morphine preference after prolonged forced abstinence
Location:Hall A-C
Presentation Time:Saturday, Nov 15, 2008, 4:00 PM - 5:00 PM
Authors:*K. A. RICHARDSON, P. T. KNACKSTEDT, G. ASTON-JONES;
Dept Neurosci, Med. Univ. South Carolina, Charleston, SC
Abstract:

We previously demonstrated that Fos activation in VTA-projecting, lateral hypothalamus (LH) orexin (hypocretin) neurons correlates with morphine preference, supporting the view that the VTA is an important site of action of LH orexin neurons in reward processing and drug abuse. Additionally, animals that undergo prolonged forced abstinence from morphine have a higher degree of Fos activation of LH orexin neurons that project to the VTA than control animals when tested for morphine preference. The purpose of the present study was to determine if this phenomenon is exclusive to LH orexin neurons or if enhanced activation of more medially located orexin neurons (in peri-fornical, PeF, or dorsomedial hypothalamus, DMH) that project to the VTA also occurs. Adult male Sprague-Dawley rats received a unilateral injection (300-350 nl) in VTA of the retrograde tracer wheat germ agglutinin conjugated to apo-horseradish peroxidase and coupled to colloidal gold (WGA-Au). Animals were subcutaneously implanted with two 75 mg morphine or placebo pellets 7 days after VTA injections. CPP conditioning (3 days, 10 mg/kg morphine per injection or saline in a balanced design) was conducted 2 weeks after pellet removal and a drug-free CPP test was conducted the day after the third conditioning session. Animals were euthanized 90 min after the CPP test and brain tissue was prepared for visualization of WGA-Au, Fos and orexin in the same neurons. Animals that underwent CPP conditioning during protracted morphine abstinence (morphine-pelleted subjects) exhibited an enhanced preference for the morphine-associated environment on the CPP test day compared to placebo-pelleted rats (as previously reported by our lab; n=8 per treatment group). The percentage of VTA-projecting LH orexin neurons in withdrawn rats that were Fos+ was positively correlated with the s of conditioned preference (r=0.743, p<0.05, n=6). In contrast, no such correlation was observed for VTA-projecting orexin neurons that were Fos+ in the PeF (r=0.044 morphine, r=-0.411 placebo) or DMH (r=-0.24 morphine, 0.434 placebo). These results support the idea that a functional dichotomy exists for subpopulations of orexin neurons, and that VTA-projecting LH orexin neurons are involved in reward processing.

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Title:Increased preference for cocaine during protracted forced abstinence: Relationship with orexin / hypocretin neurons
Location:Hall A-C
Presentation Time:Saturday, Nov 15, 2008, 2:00 PM - 3:00 PM
Authors:*G. S. ASTON-JONES1, S. LIU1,2;
1Dept Neurosci, Med. Univ. South Carolina, Charleston, SC; 2Ningbo Addiction Res. and Treatment Ctr., Ningbo, China
Abstract:Addiction is often described as a chronic relapsing disorder, in which craving and relapse to drug seeking occur even after prolonged abstinence. Our lab previously found that chronically morphine-pretreated, abstinent rats show stronger preferences for morphine-associated environments than placebo-pretreated rats (Harris et al., Neuropsychopharmacology 2003), and that this elevated drug preference was associated with increased Fos expression in orexin (hypocretin) neurons in lateral hypothalamus (LH). Here, we investigated the effects of chronic cocaine treatment followed by protracted forced abstinence on the rewarding properties of cocaine. Rats were initially treated chronically with daily injections of cocaine (10 days of escalating doses of cocaine, 10-30 mg/kg, ip). Following 2 weeks of forced abstinence from cocaine, rats were subjected to a 3-day conditioned place preference procedure for cocaine (10 mg/kg, ip). We found that cocaine preference in abstinent rats was significantly elevated compared with saline-pretreated rats (abstinent rats vs saline rats: 250.5±23.9 sec vs 132.0±44.3 sec, cocaine-paired side minus saline-paired side, p<0.01). These data suggest that like morphine, prior cocaine exposure and abstinence also has prolonged effects on the rewarding properties of drug, consistent with our previous findings (Harris and Aston-Jones, Psychopharmacology, 2001). Tissue from these animals is now being processed to examine Fos induction in LH orexin neurons. We predict that, as with protracted morphine abstinence, we will observe increased Fos expression in LH orexin neurons with protracted cocaine abstinence. This would support the view that LH orexin neurons play an important role in reward processing and addiction for both opiates and stimulants.
Title:A novel hippocampal projection to the ventral tegmental area: anatomical and electrophysiological analyses
Location:Hall A-C
Presentation Time:Sunday, Nov 16, 2008, 8:00 AM - 9:00 AM
Authors:*A. H. LUO1, R. A. WISE1, C. R. LUPICA2, G. ASTON-JONES3;
1Behav Neurosci Br., 2Cell. Neurobio. Br., NIH/NIDA/IRP, Baltimore, MD; 3Med. Univ. of South Carolina, Charleston, SC
Abstract:Neurons in the ventral tegmental area (VTA) are critical for the processing of information associated with both natural rewards and abused drugs. While drugs of abuse have direct pharmacological effects on the brain’s reward circuitry, a learned association between an organism’s environment and the perception of its internal state during drug-taking can develop, and provide a powerful and long-lasting impediment to abstinence from these drugs. Accordingly, drug addiction has been hypothesized to be resistant to extinction due to the development of a maladaptive form of learning and memory. Although there are strong behavioral data to support this hypothesis, the neuronal circuitry underlying the interaction between memory and reward systems is not well understood. Here we present anatomical data demonstrating indirect neuronal projections from the hippocampal formation (an area critical to multiple forms of memory) to the VTA, and electrophysiological data demonstrating the modulation of VTA neuron activity through activation of these hippocampal afferents. The retrograde, transneuronal tracer Pseudorabies virus (PRV; Bartha strain) was microinjected into VTA. A time-course analysis of PRV labeling was performed with survival times of 24, 36, 48, 60 and 72 hrs. The hippocampal CA3 subfield was bilaterally labeled at 48hrs, consistent with the existence of an indirect projection to VTA. The CA3 area was also the only major hippocampal subfield labeled at 48hrs, suggesting that it is the most proximal hippocampal afferent to VTA. Bilateral ibotenic acid lesions of the caudal-dorsal aspect of lateral septum (LS) one week prior to VTA PRV injections significantly reduced PRV labeling in both ipsilateral and contralateral dorsal CA3, by 78.6 and 83.8%, respectively. This suggests that the LS is an intermediary nucleus in the CA3 to VTA projection. In preliminary single-unit electrophysiological studies in urethane-anesthetized rats, we found that the majority (63.2%; 24 of 38 cells, 9 animals) of recorded VTA neurons phasically responded to electrical stimulation of CA3 in a frequency-dependent manner. Of the neurons that responded to stimulation, 87.5% (21 of 24 cells) were inhibited. Based on these data, we propose that a functional neuronal projection exists from hippocampal CA3 to the VTA, and that this projection may convey critical information regarding environmental context to brain reward systems through the VTA.
Title:Two components of phasic activity in the locus coeruleus
Location:Hall A-C
Presentation Time:Tuesday, Nov 18, 2008, 8:00 AM - 9:00 AM
Authors:*N. SAITO, J. RAJKOWSKI, G. ASTON-JONES;
Dept Neurosci, Med. Univ. of South Carolina, Charleston, SC
Abstract:Previous studies have shown that noradrenergic neurons in locus coeruleus (LC) are phasically activated shortly following salient sensory stimuli. We recently reported that phasic LC activity in monkey exhibited two components: an early response linked to sensory stimuli and a later (larger) response linked to behavioral responses and associated with decision processes. Here, we investigated whether LC phasic activity influenced behavioral outcome. Two monkeys were trained to perform a color-reward association task. In this task, two differently colored cues were displayed on the right and left sides of a fixation point on the video monitor, and one of the colors was associated with reward (juice). The animal was required to release either the left or right lever to obtain reward based on the position of the target color. The color-reward association was arbitrary across blocks of trials, and the monkey was required to find the target color by trial and error in each block of trails (blocks were 15 correct trials in length). During task performance, LC neurons showed both sensory (short-latency, ~100 msec post-stimulus) and premotor-related activities (longer-latency, ~200-300 msec pre-lever response). We found that the amplitude of the early (sensory-related) component of LC phasic responses was related to behavioral response time, such that larger early LC responses were associated with faster behavioral responses (p<.05). No significant relationship with behavioral responses was found for the premotor component of LC phasic activity. These results support the view that LC phasic activity facilitates behavioral responding and execution of decisions.
Title:Monoiodothyronamine (T1AM), an endogenous derivative of thyroid hormone, binds and activates locus coeruleus (LC) neurons
Location:Hall A-C
Presentation Time:Wednesday, Nov 19, 2008, 3:00 PM - 4:00 PM
Authors:*H. S. GOMPF1, J. H. GREENBERG2, G. ASTON-JONES4, A. IANCULESCU5, T. S. SCANLAN6, M. B. DRATMAN3;
1Neruology, Harvard, Boston, MA; 2Neurol., 3Med., Univ. of Pennsylvania, Philadelphia, PA; 4Neurosci., Med. Univ. of South Carolina, Charleston, SC; 5Biochem. and Biophysics, Univ. of California, San Francisco, San Francisco, CA; 6Physiol. and Pharmacol., Oregon Hlth. & Sci. Univ., Portland, OR
Abstract:The proposal that 3, 3' 5 L-triiodothyronine (T3) may give rise to a series of amines which could act as adrenergic co-transmitters, mediating the autonomic effects of thyroid hormone, has been under investigation for several decades. A morphological basis for the mounting biochemical and physiological evidence in support of that hypothesis was provided by autoradiography (ARG) and immunohistochemistry showing that the proposed amino acid precursor, T3, is taken up by the locus coeruleus (LC) from which it and its metabolites are axonally transported to adrenergic targets throughout the brain. Scanlan et al (NATURE MEDICINE '04) have now discovered and characterized the first endogenous thyronamine: 3-monoiodothyronamine (T1AM). Its role has only been investigated pharmacologically given the large doses required to elicit its actions as an adrenergic antagonist. These actions and other considerations have led to a reasonable view of T1AM as a metabolite of reverse T3 (rT3) rather than T3. We considered that a physiological role for T1AM, not revealed by previous methods for assessing its potency, seemed possible, particularly in light of its yet untested potential for moderating hyperadrenergic states in hyperthyroidism, a state in which rT3, as well as T3, is markedly over-produced. METHODS: Film ARGs, prepared 1 and 3 hours after intra-arterial (i.a) injection of high sp. activity I125-T1AM, were correlated with histology to determine whether T1AM binds to the LC in vivo. Single unit LC neuronal activity was recorded in anaesthetized rats before and during local microinjection of T1AM. RESULTS: Binding to the LC after an i.a injection of I125-T1AM was demonstrated by film ARG. Most interesting was the observation that T1AM injected directly into the LC caused robust, significant and dose-dependent increases in LC firing rates in doses as low as 3 nM, a dose several orders of magnitude smaller than that required for observing any T1AM effects after intraperitoneal or intrathecal injection. CONCLUSIONS: T1AM may serve physiologic functions in the central noradrenergic nervous system. Choice of the LC as a target for demonstrating the binding and activity of this amine allowed a better approximation of its ability to act in doses close to the physiological range. Further insight into its role in autonomic function may come from investigating its potency in rats with altered thyroid function. Overall the results suggest that there is a family of thyroid hormone-derived neuroactive amines. LC binding and behavior may serve as a screening tool for detecting members of such a family.